Immunoassays have been developed based on a number of different methodologies for detecting a wide variety of analytes. Most of the assay methods require a skilled technician and laboratory equipment. Although there is a need for assays which can be performed in the field, only a few assays have been successfully adapted. For example, an enzyme-linked immunosorbent assay (ELISA) for determining levels of hormone indicative of pregnancy has been marketed for home use. However there is a need for an assay for field use for other types of applications such as for testing urine for controlled substances, water for pollutants, or milk for antibiotics. In addition to being fast and easy to perform and requiring little or no equipment to prepare and analyze, the assays must be sensitive and accurate.